Sciencemadness Discussion Board

Chlorine released?

rollercoaster158 - 6-5-2012 at 07:24

I had some thin iron rods, and no use for them. I decided to make some iron oxide, so I stuck them in a salt (NaCl) solution. A week later, there was plenty of orange/red iron oxide in the container, but the faint smell of chlorine. Does iron/iron oxide cause NaCl to decompose into sodium and chlorine? It's not a lot of chlorine, but a detectable amount that I am curious about.

hissingnoise - 6-5-2012 at 07:45

Something in the water?

CrEaTiVePyroScience - 6-5-2012 at 07:53

Well I think I can answer this question , because I have also made iron oxide that way and got some youtube videos about but anyways back to topic.
You added NaCl to the water to increase its conductivy because you are running electric current through it.
There are several reactions happening:

1. 2 H2O -> 2 H2 + O2 the water is splitting up in two gasses, hydrogen and oxygen due to electrolysis the oxygen causes the iron nails which are acting as cathodes and anodes to rust. (Rusting is nothing more then something being exposed to oxygen Fe + 3 O2 --> 1 Fe2O3.) So the O2 gas is escaping on the nail and running over it , causing it to rust.

2. NaCl is splitting up in chlorine gas due to the electrical current and will produce chlorine gas, the amounts of the gas should not be underestimated. At the start most of the gas will dissolve in the water, creating bleach but when the water is saturated with the gas, the gas will escape.

SOLUTION: To make the iron oxide you don't have to use NaCl to increase the conductiviy of the water but you can also add somethingelse , I am sorry I can't remember the name of the product that I added because its too long ago but you can google it!

[Edited on 6-5-2012 by CrEaTiVePyroScience]

blogfast25 - 6-5-2012 at 08:20

Quote: Originally posted by CrEaTiVePyroScience  

You added NaCl to the water to increase its conductivy because you are running electric current through it.

[Edited on 6-5-2012 by CrEaTiVePyroScience]

Creative: rollercoaster makes no mention of a current (even though that is a common hobbyist way of making ferric oxide).

I have a much simpler explanation: anyone who has handled solutions of ferric compounds will attest to a specific odour, I’m not sure what causes it. But it’s somewhat reminiscent of faint chlorine and could be easily mistaken for it. Unless you have other evidence that you’re observing actual chlorine, that is the most likely explanation…

Chlorine solutions can be detected by adding them to potassium iodide solution with some soluble starch mixed in: 2 I<sup>-</sup> + Cl<sub>2</sub> == > I<sub>2</sub> + 2 Cl<sup>-</sup>. Starch forms a deep blue complex with iodine, detectable even at low iodine concentrations.

CrEaTiVePyroScience - 6-5-2012 at 08:44

@Blogfast25 Oh that's right looks like I read to fast ,sorry for that.

@rollercoaster158 But its quite awkward to make iron oxide with a NaCl solution and without current? I mean if you use current your yield would be ALOT higher. Just adding 4.5v will atleast tripple your yields perhaps even more.
Another way to find out is to add just normal food coloring or ink to the water before you let it stand for a week. If after a week, the solution has lost (some) color, it indicates that chlorine gas was produced. (Even small amounts of chlorine gas will make the water lose it's color)

[Edited on 6-5-2012 by CrEaTiVePyroScience]

bbartlog - 6-5-2012 at 09:38

Although no voltage was applied, there may still be a small internally generated current. Iron is attacked by atmospheric oxygen, O2. The oxygen in tearing the electrons from the iron might generate enough of a potential that in some places Cl- would in turn lose an electron, being oxidized to Cl. Certainly there has to be some reduction or oxidation of Na+ and/or Cl- taking place, else what role would it be playing in accelerating this reaction?

rollercoaster158 - 6-5-2012 at 10:42

Yes, I know that I can assist production by adding a current. However, I had a lot of time to do it and decided to skip that. I have no means to tell whether it's chlorine, it just smells like chlorine. It could have been the iron oxide, who knows. By the looks of it it's red iron oxide (Fe2O3).

AndersHoveland - 6-5-2012 at 23:00

I am very doubtful that any chlorine was produced in your reaction. But it is not entirely beyond the realm of possibility. Fe+2 ion solvated in water could potentially react with oxygen from the air to transiently form complexed superoxide as an intermediate. It could be possible that this superoxide is oxidizing some of the chloride ions to chlorine.

If this is actually correct, the formation of chlorine would only be a very small part of the overall reaction. Most of the chlorine would just rapidly oxidize the iron, and be reduced back to chloride, but some of it might be able to escape.

woelen - 6-5-2012 at 23:08

I'm absolutely sure that no chlorine was formed in this reaction, not even a trace. Chlorine is very reactive and certainly is not formed spontaneously under the conditions you describe. It might be some impurity in the iron, the salt or the water, which gives a similar smell.

An interesting test may be to make a very small amount of real chlorine and compare its smell with your salt/iron smell. Take 1 big drop of bleach and one big drop of acid (e.g. dilute hydrochloric acid) and add these to each other in a glass or plastic cup and carefully smell the cup. DO NOT USE MORE THAN SINGLE DROPS. You'll notice the chlorine, even from this single drop. Compare this with the smell from your salt/iron setup. Are they really the same?

[Edited on 7-5-12 by woelen]

hissingnoise - 7-5-2012 at 04:14